fix(chisel): convert seed to private key file EE-5099

main.go

@@ -109,6 +109,11 @@ var serverHelp = `
     of man-in-the-middle attacks (defaults to the CHISEL_KEY environment
     variable, otherwise a new key is generate each run).
 
+    --private-key-file, An optional path to a PEM-encoded TLS private key. When 
+    this flag is set, the --key option is omitted, and the provided private key 
+    is used to secure all communications. A private key file can be generated by:
+    openssl ecparam -name prime256v1 -genkey -out private_key.pem
+
     --authfile, An optional path to a users.json file. This file should
     be an object with users defined like:
       {
@@ -170,6 +175,7 @@ func server(args []string) {
 
 	config := &chserver.Config{}
 	flags.StringVar(&config.KeySeed, "key", "", "")
+	flags.StringVar(&config.PrivateKeyFile, "private-key-file", "", "")
 	flags.StringVar(&config.AuthFile, "authfile", "", "")
 	flags.StringVar(&config.Auth, "auth", "", "")
 	flags.DurationVar(&config.KeepAlive, "keepalive", 25*time.Second, "")

server/server.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httputil"
 	"net/url"
+	"os"
 	"regexp"
 	"time"
 
@@ -22,14 +23,15 @@ import (
 
 // Config is the configuration for the chisel service
 type Config struct {
-	KeySeed   string
-	AuthFile  string
-	Auth      string
-	Proxy     string
-	Socks5    bool
-	Reverse   bool
-	KeepAlive time.Duration
-	TLS       TLSConfig
+	KeySeed        string
+	AuthFile       string
+	Auth           string
+	Proxy          string
+	Socks5         bool
+	Reverse        bool
+	KeepAlive      time.Duration
+	TLS            TLSConfig
+	PrivateKeyFile string
 }
 
 // Server respresent a chisel service
@@ -73,11 +75,23 @@ func NewServer(c *Config) (*Server, error) {
 			server.users.AddUser(u)
 		}
 	}
-	//generate private key (optionally using seed)
-	key, err := ccrypto.GenerateKey(c.KeySeed)
-	if err != nil {
-		log.Fatal("Failed to generate key")
+
+	var key []byte
+	var err error
+	if c.PrivateKeyFile != "" {
+		//read private key from the file specified by the --private-key-file flag
+		key, err = os.ReadFile(c.PrivateKeyFile)
+		if err != nil {
+			log.Fatal("Failed to read private key from disk")
+		}
+	} else {
+		//generate private key (optionally using seed)
+		key, err = ccrypto.GenerateKey(c.KeySeed)
+		if err != nil {
+			log.Fatal("Failed to generate key")
+		}
 	}
+
 	//convert into ssh.PrivateKey
 	private, err := ssh.ParsePrivateKey(key)
 	if err != nil {

share/ccrypto/determ_rand.go

@@ -34,7 +34,15 @@ func (d *determRand) Read(b []byte) (int, error) {
 	for n < l {
 		next, out := hash(d.next)
 		n += copy(b[n:], out)
-		d.next = next
+
+		// In Golang 1.20, ecdsa.GenerateKey() introduced a function called
+		// MaybeReadRand() which reads 1 byte from the determRand reader
+		// with 50% chance. As a result, GenerateKey() generates
+		// nondeterministic keys.
+		// The following conditional check neutralizes this effect.
+		if l > 1 {
+			d.next = next
+		}
 	}
 	return n, nil
 }